The present invention is generally directed to electronic circuit breakers and similar devices for use in direct current systems. More particularly, the present invention is directed to a circuit breaker which provides a substantially constant impedance, as seen from the load, under varying load conditions. Additionally, the present circuit breaker is actuated by a combination of circuit conditions including not only current level but also current overload duration.
In large mainframe computer systems, there are typically provided a number of direct current power supply units. During routine maintenance situations, it often becomes necessary to turn off one or more banks of these power supply units. When mechanical circuit breakers are employed for this purpose, it is easily possible to turn off an incorrect circuit. Such activities often only compound problems which may exist. Additionally, for certain mechanical breakers, it is difficult to discern whether they are on, off, or have been tripped. Electronic circuit breakers do not necessarily exhibit these problems.
However, when a mechanical circuit breaker is replaced by an electronic circuit breaker, one must also be concerned with circuit behavior during varying load conditions which do not in fact result in overcurrent conditions and in particular do not result in overcurrent conditions which cause the circuit breaker to be "tripped". In particular, under conditions of varying load, when an electronic circuit breaker is employed, it is desirable to be able to provide a circuit which exhibits constant impedance properties as seen by the load, even under varying load conditions.
The use of an electronic circuit breaker would also provide important signal and control advantages. In particular, it would be desirable to have an electronic circuit breaker which could be addressed by name or by other designations from a computer keyboard or from another console device. Likewise it would be desirable to have information concerning the "on" or "off" status of the device being protected and/or indications to whether or not the circuit breaker has experienced a sufficiently large prior overcurrent condition to have caused an earlier fault interruption.